Rationale: Amyloidogenic processing of beta-amyloid precursor protein (APP) leading to the formation of beta amyloid (Abeta) is a key event in the pathogenesis of Alzheimer's disease (AD). Abeta is sequentially derived by a cleavage at the residues 671/673 by beta-site APP cleaving enzyme, followed by a cleavage at the residues 711/713 by gamma-site APP cleaving enzyme. Point mutations in APP such as in Swedish double mutations, are known to promote beta-site cleavage. Therefore, we hypothesize that antisense blocking of the mutated beta-site, and not of the normal gamma-site, will reduce translation of amyloidogenic APP-mRNA but not normal APP-mRNA, in a model harboring Swedish mutations (KM670/671NL) (TgAPPSWE or Tg2576). We tested this hypothesis in Tg2576 (TgAPPSWE) transgenic mice by blocking translation of APP-mRNA with 2'-Methoxy-O-Ethyl (MOE)-modified antisense oligodeoxynucleotides (ODNs) directed at the mutated beta-and normal gamma-sites. The data show that 2'MOE modified antisense ODNs directed at the beta-site significantly reduced cerebral levels of soluble Abeta40/42 (sAbeta40/42) while the levels of total detectable alpha-cleaved soluble APP (sAPPalpha) showed a small increase [Siegel and Chauhan, SFN-2002, 687.14]. Antisense blocking at the gamma-site did not produce any effect. These results indicate that beta-site blocking may have arrested the translation of amyloidogenic but not mouse APP, while gamma-site blocking is non-specific. Based on these results, current application proposes the use of a Swedish double mutant model (TgAPPSWE) harboring point mutations in APP (K670M/N671L), and a model overexpressing normal wild type human APP (TgAPPWT) as a control to test the efficacy of antisense ODNs directed at the beta-site of mutated APP in reducing amyloid burden and amyloid-associated toxicity. This project is to test the potential usefulness of antisense ODNs to the beta-site as therapy for familial AD. Hypothesis: Antisense blocking at the mutated beta-site will inhibit the translation of amyloidogenic APP without affecting normal APP processing in TgAPPSWE and TgAPPWT. Specific Aims: 1. Determine if antisense blocking at the mutated beta-site will reduce the levels of detectable mutated amyloidogenic APP-mRNA without affecting mouse APP-mRNA and production of normal alpha-cleaved APP in TgAPPSWE or normal human and mouse APP-mRNA in TgAPPWT as evaluated by cRT-PCR quantitation of normal and mutant APP-mRNA and ELISA measurement of sAPPalpha. 2. Determine if antisense blocking at the mutated beta-site will reduce cerebral amyloid load in TgAPPSWE, as evaluated by ELISA and immunocytochemistry of Abeta peptides. 3. Determine if antisense blocking at the mutated beta-site will prevent and reverse Abeta-induced synaptotoxicity and the neurotoxic response of microglia and astroglia in TgAPPSWE, as evaluated by immunocytochemistry and imaging analysis of synaptic markers and markers of reactive microglia and astroglia. Significance: Targeting the translation of amyloidogenic APP by antisense synthetic oligodeoxynucleotides may prove to be an effective and safe form of gene therapy for treating familial AD and other genetic diseases.